The present invention relates to a portable electronic apparatus, and more particularly to a portable electronic apparatus having an audible annunciator, such as a loudspeaker, and an alarm lamp.
A portable electronic apparatus, such as a pager receiver, having a function to alarm or to notify its bearer, is equipped with an audible annunciator, such as a loudspeaker, for alerting the bearer. In the case of a pager receiver, the sound of its loudspeaker informs its bearer that he is being paged. However, in those cases where a plurality of receivers are used at the same time or where a receiver has to be used in an environment having a high-level of noise, it may be difficult to distinguish the sounding receiver from other sounds. Also, the pagee may fail to notice the sound. As a solution to these problems, some paging receivers are equipped with an alarm lamp in addition to a loudspeaker. The loudspeaker and lamp are turned on simultaneously with the activation of the annunciator. An example of such a pager receiver is disclosed in U.S. Pat. Nos. 3,783,384 and Re. 28,222.
A light emitting diode (LED) is usually employed as the alarm lamp. The activation of this LED requires about 1.5 volts. However, because a radio pager receiver or the like is ordinarily powered by a single dry battery of 1.2 to 1.7 volts, to reduce its size, the dropping of the battery's voltage may disable the LED. To avoid this trouble, the inductance of the driving coil in the loudspeaker is used to generate counter-electromotive forces at both ends of the indictance element, these forces being utilized to turn on and off the LED.
On the other hand, if the receiver has to be used in a quite evnironment, it will be desirable to alert the bearer of the receiver merely by turning on the lamp without giving any sound. Unlike the above cited instance, the loudspeaker inductance elements cannot be used to add a counter-electromotive force during this function. Another inductance element will have to be provided exclusively for the lamp and arranged to be switched on and off, as required. However, the additional inductance element is not advisable for a portable electronic apparatus which is small and light.